Of the two luminaries that dominate our sky, it is the moon that is of particular interest to the Lunar Reconnaissance Orbiter (LRO) project. The LRO will travel to the moon in late fall 2008, mapping the surface to help pave the way for humans to return.

NASA wants to explore the Moon's polar regions for many reasons, not the least of which is that deep polar craters may contain ice. However, the instability of polar orbits poses a real problem for exploration and communication with Earth.

A pivoted catch designed to fall into a notch on a ratchet wheel so as to allow movement in only one direction (e.g. on a windlass or in a clock mechanism), or alternatively to move the wheel in one direction.